The Three Hundred Project: Substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters

Roan Haggar,Gustavo Yepes,Meghan E Gray,Frazer R Pearce,Alexander Knebe

doi:10.1093/mnras/stab064

Abstract

ABSTRACT Dark matter-only simulations are able to produce the cosmic structure of a Lambda cold dark matter universe, at a much lower computational cost than more physically motivated hydrodynamical simulations. However, it is not clear how well smaller substructure is reproduced by dark matter-only simulations. To investigate this, we directly compare the substructure of galaxy clusters and of surrounding galaxy groups in hydrodynamical and dark matter-only simulations. We utilize thethreeHundred project, a suite of 324 simulations of galaxy clusters that have been simulated with hydrodynamics, and in dark matter-only. We find that dark matter-only simulations underestimate the number density of galaxies in the centres of groups and clusters relative to hydrodynamical simulations, and that this effect is stronger in denser regions. We also look at the phase space of infalling galaxy groups, to show that dark matter-only simulations underpredict the number density of galaxies in the centres of these groups by about a factor of four. This implies that the structure and evolution of infalling groups may be different to that predicted by dark matter-only simulations. Finally, we discuss potential causes for this underestimation, considering both physical effects, and numerical differences in the analysis.

Highlights

Cosmological simulations are a valuable tool in testing predictions of the Λ cold dark matter (ΛCDM) model of the Universe, widely accepted as the ‘standard model’ of cosmology (Diemand & Moore 2011; Frenk & White 2012)
We look at the phase space of galaxies in groups that are on their first infall into a cluster, to study how this distribution is affected by the inclusion of baryonic material in simulations
Tidal effects were partly responsible for the over-merging problem, as seen in early simulations (Moore et al 1998). If these tidal effects are enhanced in dark matter-only simulations relative to hydrodynamical simulations, this could result in a drop in the number density of galaxies in denser regions, causing the deficit of galaxies seen in the centres of groups and clusters

Summary

Introduction

Cosmological simulations are a valuable tool in testing predictions of the Λ cold dark matter (ΛCDM) model of the Universe, widely accepted as the ‘standard model’ of cosmology (Diemand & Moore 2011; Frenk & White 2012). In this paradigm, small haloes form via the gravitational collapse of cold dark matter. The mass composition of galaxy clusters is dominated by dark matter, which makes up over 80% of the mass of a typical cluster (Allen et al 2011), and so the gravitational collapse of these structures is dominated by the effects of dark matter (Jenkins et al 1998; Springel et al 2005; Borgani & Kravtsov 2011)

Results

Discussion

Conclusion